British patent Spec. No. 1,372,116 describes the preparation of fibril-like materials suitable for the manufacture of waterlaid sheets. Such products are prepared from ultra high molecular weight olefin polymers and are referred to as fibrils. Such fibrils are prepared by feeding a hydrocarbon solution of the olefin polymer to a special type of apparatus in which the hot polymer solution is subjected to high shear forces, and subsequently cooled to precipitate highly-oriented fibrils of the olefin polymer from the hydrocarbon.
The preparation of the hot hydrocarbon solutions of such olefin polymers for use in the process of British patent Spec. No. 1,372,116 presents difficult technical problems. By reason of the ultra high molecular weight of the olefin polymers employed in the process, such polymer solutions have very high viscosities at low concentrations of the olefin polymer. The high viscosities of such polymer solutions makes it difficult to provide adequate stirring to assist in dissolving all of the olefin polymer. It is essential to dissolve all of the olefin polymer in the hydrocarbon solution, as it has been observed that the presence of even minute quantities of undissolved olefin polymer in the polymer solution has an adverse effect upon the quality of the ultimate fibrils prepared therefrom.
To facilitate the preparation of hydrocarbon solutions of such olefin polymers, it has been proposed to ameliorate the problem of dissolving the polymer by comminuting the olefin polymer to very small particles to accelerate its rate of dissolution in the liquid hydrocarbon. Notwithstanding this technique, difficulties in dissolving all of the polymer particles are still presented. It is believed that the difficulty results from the fact that the fine polymer particles imbibe hydrocarbon at their surface and swell to a volume substantially larger than the original size of the polymer particles. The surfaces of such swollen polymer particles tends to be quite tacky and, when such swollen polymer particles contact each other, they tend to fuse together and form agglomerates of the swollen polymer particles. Apparently the rate of diffusion of the liquid hydrocarbon into such agglomerates is slow.